The present invention relates to an edible coating for food products. More particularly, this invention relates to an edible moisture barrier capable of inhibiting the migration of moisture through the surface of a food product. The moisture barrier is particularly useful in preventing moisture migration within a multi-component food product between components having different water activities.
For many food products, particularly cooked food products, critical levels of moisture must be maintained if the product is to exhibit optimum quality and acceptable safety. Moisture migration in finished food products can seriously compromise quality, stability and safety. For example, the loss of moisture out of food products having a relatively high moisture content, such as brownies or cookies, dries out these foods and they are perceived as having lost their freshness. Similarly, absorption of moisture from the surrounding atmosphere into a food product normally having a low moisture content, such as a cracker, can cause the food product to become soft, losing the desired crispness associated with the fresh product. In addition, many chemical and enzymatic deteriorative reactions proceed at rates partially governed by the moisture contents of foods. Excessive rates of these reactions can promote deleterious changes in the flavor, color, texture, and nutritive value of food products.
In a multi-component food product, particularly whose various components have different moisture contents and water activities such as, for example, a glazed doughnut, a sandwich, or a pie composed of a pie crust and a filling, the moisture can migrate between adjacent components, altering the character of several of the food product's components. For example, in a glazed doughnut, the glazing can absorb water from the fried dough body, becoming sticky and moist. At the same time, the dough body loses moisture, becoming dry.
In addition to compromising the quality of finished food products, moisture migration can hinder production and distribution of food products. For example, as the glazing on a doughnut absorbs moisture from the fried doughnut, the glazing deteriorates and becomes sticky.
Of the various methods of affecting moisture migration known in the art, coating the food product with an edible moisture barrier holds much promise. To have utility, the barrier should have a low permeability to moisture, in order to prevent the migration of water or water vapor. In addition, the barrier should cover the food surface completely, including crevices and adhere well to the food product surface. The moisture barrier should be sufficiently strong, soft and flexible to form a continuous surface that will not crack upon handling, yet can be easily penetrated during consumption. In addition, the barrier film's organoleptic properties of taste, after taste and mouth feel should be imperceptible, and there should be no awareness of the barrier when it is being bitten through. Finally, the moisture barrier should be easy to manufacture and easy to use.
Because lipids, such as, for example, oils, fats and waxes, are composed of water insoluble molecules capable of forming a water impervious structure, they have been investigated for use in moisture barrier films. With respect to oleaginous materials (fats and oils), it has been shown that, unless an undesirably thick coating is used, the barrier is ineffective. Wax barriers have disadvantages as moisture barriers because they tend to crack upon handling or with changes in temperatures. Accordingly, many of the barriers in the art use a water-impermeable lipid in association with hydrocolloids (polysaccharides) such as alginate, pectin, carrageenan, cellulose derivatives, starch, starch hydrolysates and/or gelatin to form a gel structure that provides a crosslinked semi-rigid matrix to entrap and/or immobilize the nonaqueous material. In many cases these components are formed as bilayer films to provide water impermeability. These bilayer films may be precast and applied to a food surface as a self-supporting film with the lipid layer oriented toward the component with highest water activity (w.sub.a). See, for example, U.S. Pat. No. 4,915,971 and PCT Publication No. 86/00501 (both to Fennema); U.S. Pat. No. 4,880,646 (Lew); and Greener et al. (1989) Journal of Food Science, vol. 54, pp. 1393-1399 and 1400-1406.
There are, however, a number of drawbacks associated with these barriers. The hydrocolloids themselves are water soluble and tend to absorb water with time. In addition, some hydrocolloids tend to make the barriers fairly stiff, requiring the addition of a plasticizer to increase flexibility. Furthermore, the thickness of some of these barriers may make their presence perceptible when they are being bitten through.
Another method is to use crosslinked, refined shellac for the matrix, see, for example, U.S. Pat. No. 4,710,228 to Seaborne, or to form microemulsions of fats and water, see, for example, U.S. Pat. No. 4,603,051 to Rubenstein. However, the water permeability of both these types of barriers is fairly high, and the coatings are undesirably thick to overcome this significant permeability.
None of the edible moisture barriers of the art have succeeded in providing all of the requirements for a thin effective moisture barrier that is imperceptible to taste. Accordingly, it is an object of this invention to provide a thin edible moisture barrier consisting essentially of oleaginous materials and wax which is essentially imperceptible to taste and which is useful as a barrier to moisture migration in or out of a food product. Another object includes providing a moisture barrier which is capable of inhibiting the migration of moisture between components of a multi-component food product, particularly between adjacent components having different water activities. Another object of the invention is to provide methods of coating surfaces of a food product with a moisture barrier which are rapid and which are particularly suited to automated production methodologies used in industrial scale food production.
Other objects of the invention will in part be obvious and will in part appear hereinafter.